Irrigation 101

Brian E. Vinchesi

PART 3: IRRIGATION SYSTEM INSTALLATION

In many states, the law requires that only licensed plumbers install
backflow preventers and tap into the potable water supply. Many times, an
irrigation contractor purchases the backflow preventer and has a plumber
install it; a large irrigation contractor may have a full-time plumber on
staff.

Each type of backflow preventer has strict installation requirements. Some
types of preventers (pressure vacuum breakers and reduced-pressure type)
will dump water when contaminated. Therefore, you need to install the
device outside, with a catch drain or in a drainable room so flooding does
not occur. For smaller systems, install backflow preventers with copper
pipe inlets and outlets. Units larger than 3 inches are installed on steel
or ductile iron piping.

You can install pipe either by pulling or trenching. This again will depend
on the size, type of pipe and geographical preferences. Pipe 2 inches and
less is often pulled. Polyethylene is piped more commonly than PVC.

Install pipe deep enough so that maintenance practices will not damage it,
but not so deep that you can't service it. The trench you use should be
free from rock and other debris. Install the pipe in a consistent manner
with no sharp turns. Glue the fittings per the manufacturer's requirements.
It is a good idea to double-clamp polyethylene fittings.

Wire is not pulled, but laid. Never pull wire directly off the roll; it
will go in too tight. It is important to install the wire with plenty of
slack, especially at valve boxes to allow for servicing. Install wire
beside or below the pipe to prevent damage. Place 24-volt wire and 120-volt
wire on separate sides of the trench.

Install valve boxes at grade and, where possible, in landscaped areas where
you can cover them with mulch. Make sure covers are intact and securely
fitted to the box.

Height of sprinklers

Install sprinklers flush to grade so that mowing or other maintenance will
not damage them. Sprinklers installed too low will have their streams
affected by the turf. Sprinklers installed too high are subject to damage
from traffic and mowers, and can pose a tripping liability.

You can install sprinklers on a number of support devices, but it is
important that there not be a rigid connection between the sprinkler and
the pipe. This causes the force of any weight going over the sprinkler,
such as the mower, to be transmitted directly to the pipe, which can cause
the pipe or fitting to break. Use a flexible connection such as a swing
joint or swing-pipe assembly.